ges-xml-formatter: use g_ascii_dtostr() instead of messing with setlocale()

Libraries shouldn't use setlocale().
container: Do not forget to initialize the timeline before using it
ges-source: Move sub element handling to the base class.

	    + And port all the subclasses.
utils: Adds the create bin method there to be used internally.
test sources: Modifies the way we handle properties such as pattern.

     + This makes make check pass.
     + This standardizes property handling.
sources: Starts adding video-uri-source et al. WIP fix up on me.
Removes old uri-source
Documentation updates.
Implement audio and video source.
Port all sources to inheriting from audio / video base sources.

That was painful.
integration tests: adds a test for scaling video.
videotransition: No need to hard set width and height anymore.
Install width and height properties in ges-video-source.
framepositionner: put width and height handling there.
ges-track: Remove the set_caps from the API, keep it internally.

	   + Add restriction caps instead.
	   + gnonlin sets these caps on all its children, which
	     is not really convenient.
test-utils: Adds a utility function to quicly check the timeline.

	    + It takes a dump_to_dot argument as a free bonus.
timelineedition test: Adds a test_scaling.

		+ It will check that the clip updates its size correctly.
		+ Will certainly move elsewhere.
timeline-element: Add a set_parent vmethod

API:
        GESTimelineElment->set_parent vmethod
videosource: Make sure to update z-order when layer priority changes

Conflicts:
	ges/ges-video-source.c
Misc fixes for class hierarchy rework FIXUP